The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive that discerns the polarity of a head signal from a sync mark to enhance data detection.
FIG. 1 shows a prior art format of a disk 2 employed in a disk drive of a computer system. The disk 2 comprises a plurality of radially-spaced, concentric tracks 4 which are partitioned into a plurality of data sectors. The disk 2 further comprises a plurality of embedded servo sectors 6 for use in servoing a head over the desired track during write and read operations. A sector (data or servo) typically comprises a preamble field 8 for synchronizing timing recovery and gain control within a read channel, and a sync mark 10 for symbol synchronizing to a data field 12. Data stored in an embedded servo sector 6 may include a track address which provides coarse head positioning information to a servo control system. An embedded servo sector 6 also typically comprises a plurality of servo bursts 14 recorded at precise offsets from a track""s centerline to provide fine head positioning information to the servo control system.
Data is recorded in a sector by modulating a current in an inductive write element of a head. The magnetic field emanating from the write element magnetizes the surface of the disk along the sector. During a read operation, a read element (e.g., inductive coil or MR element) is positioned over the sector to sense the magnetic transitions representing the recorded data. The resulting read signal comprises polarity alternating pulses which are detected and demodulated into an estimated data sequence representing the recorded data sequence. The accuracy of the detection/demodulation process depends on various factors which affect the signal-to-noise ratio of the read signal (e.g., electronic and media noise, recording density, detection algorithm, etc.). It is desirable to optimize these factors to maximize the capacity of a disk drive for a given bit error rate.
The present invention may be regarded as a disk drive comprising a disk having a plurality of data tracks, each data track comprising a plurality of sectors. Each sector comprises a preamble field for storing a predetermined periodic data sequence, a sync field for storing a predetermined sync mark pattern, and a data field for storing data. A head is actuated radially over the disk for generating a read signal comprising a plurality of polarity alternating pulses. A sync mark detector detects the sync mark pattern in the read signal, wherein when the sync mark pattern is detected the sync mark detector generates a sync mark detect signal and a polarity signal. The polarity signal is indicative of an expected polarity of the pulses in the read signal representing the data stored in the data field. A data detector detects an estimated data sequence from the read signal using the polarity signal to enhance performance, and a data decoder decodes the estimated data sequence into a decoded data sequence in response to the sync mark detect signal.
In one embodiment the data stored in the data field is recorded on the disk in a binary sequence, a xe2x80x9c1xe2x80x9d bit in the binary sequence is represented by a dibit recorded on the disk the dibit generating a dibit response in the read signal, and a xe2x80x9c0xe2x80x9d bit in the binary sequence is represented by the absence of a dibit recorded on the disk. A matched filter having an impulse response substantially matched to the dibit response filters the read signal to generate a filtered signal, and a threshold detector compares the filtered signal to a programmable threshold, wherein the programmable threshold is programmed in response to the polarity signal.
The present invention may also be regarded as a method of detecting data stored in a disk drive. The disk drive comprises a disk having a plurality of data tracks, wherein each data track comprises a plurality of sectors. Each sector comprises a preamble field for storing a predetermined periodic data sequence, a sync field for storing a predetermined sync mark pattern, and a data field for storing the data. The method comprises the steps of actuating a head radially over the disk to generate a read signal comprising a plurality of polarity alternating pulses. The sync mark pattern is detected in the read signal, and when the sync mark pattern is detected, a sync mark detect signal and a polarity signal are generated. The polarity signal is indicative of an expected polarity of the pulses in the read signal representing the data stored in the data field. An estimated data sequence is detected from the read signal using the polarity signal to enhance performance, and the estimated data sequence is decoded into a decoded data sequence in response to the sync mark detect signal.